1. Field of the Invention
The present invention relates to a virtual private network system over a public mobile data network and a virtual local area network (IAN).
2. Description of the Related Art
In a first prior art virtual private network system, a data gateway is connected between an internet and a public mobile data network. Also, a router is connected between the internet and a virtual LAN.
Assume that a data terminal is connected to one LAN emulation client within the virtual LAN. In this case, when data addressed to a first IP address of the data terminal is generated in the internet, the data always reaches the data terminal.
Next, assume that the data terminal is moved from the virtual LAN to a service area of the public mobile data network. Note that the data terminal has a second IP address under the public mobile data network. Even in this case, the data terminal can receive the same data service via the internet, thus realizing a virtual private network system over the public mobile data network and the virtual LAN.
The first prior art virtual private network system will be explained later in detail.
In the first prior art virtual private network system, however, since the data terminal has two IP addresses, an originator needs to know in advance whether the data terminal is under the virtual LAN or under the public mobile data network. This makes the control complex.
In a second prior art virtual private network system, the virtual LAN is connected as a sub network to the public mobile data network. In this case, note that the data terminal has only one IP address.
In the second prior art virtual private system, even if the data terminal is moved from the virtual LAN to a service area of the public mobile data network, the data terminal can receive the same data service via the internet, thus realizing a virtual private network system over the public mobile data network and the virtual LAN.
The second prior art virtual private network system will be explained later in detail.
In the second prior art virtual private network system, however, even when one data terminal under the virtual LAN wants to transfer data to the data terminal under the public mobile data network, such data cannot be transferred to the data terminal, since the network addresses of both of the data terminals are the same as each other. Thus, it is impossible to carry out communications between the data terminals belonging to the same virtual private network system.